Source : Webster's Revised Unabridged Dictionary (1913)

Ulva \Ul"va\, n. [L., sedge.] (Bot.)
   A genus of thin papery bright green seaweeds including the
   kinds called sea lettuce.

Source : WordNet®

Ulva
     n : type genus of the family Ulvaceae; green seaweed having a
         thallus two cells thick: sea lettuce [syn: {genus Ulva}]